Activation Of Dislocation Slip Research Articles

Origin of the Anomalous {10\\bar12} Twinning during Tensile Deformation of Mg Alloy Sheet

In order to understand the origin of the anomalous twinning of the {10\\bar12} type, rolled sheets of AZ31 Mg alloy were deformed at room temperature in tension along the rolling direction. An excellent correlation was found between {10\\bar12} twinning tendency and basal dislocation slip activity. Calculation of strain tensor indicated that the diagonal strain components associated with the localized basal slip can be canceled completely by the {10\\bar12} twinning. The results led to the conclusion that anomalous {10\\bar12} twins were formed to accommodate the strain incompatibility caused by localized basal dislocation slip.

Nanoindentation measurements of the mechanical properties of polycrystalline Au and Ag thin films on silicon substrates: Effects of grain size and film thickness

This paper presents the results of nanoindentation experimental studies of the contact-induced deformation in Au and Ag thin films. The paper examines the effects of film thickness and substrate deformation restraint on the mechanical properties of electron beam (e-beam) deposited Au and Ag films. Following a brief description of film microstructure, surface topography, and contact-induced pile-up deformation, film mechanical properties (hardness and Young's modulus) were determined using nanoindentation techniques. The indentation size effects (ISE) observed in films with different thicknesses were explained using a mechanism-based strain gradient (MSG) theory. The intrinsic film yield strengths and hardnesses extracted from the MSG theory are shown to exhibit classical Hall–Petch dependence on the inverse square root of the average film grain size. Displacement bursts were also found to occur in Ag films at indentation load levels of 100 μN. These were attributed to the initial onset of dislocation slip activity, when the shear stress exceeds the estimated theoretical shear strengths of the materials.

Indentation size effects in face centered cubic single crystal thin films

This paper presents the results of an experimental study of indentation size effects in Au, Ag and Ni single crystals with (0 0 1), (0 1 1) and (1 1 1) orientations. The studies show clearly that the hardness increases with decreasing indentation size, for indents between ∼30 and 600 nm in depth. The observed size dependence is rationalized using the mechanism-based strain gradient plasticity theory by Nix and Gao. The shape and extent of material pile-up is shown to depend strongly on the material hardness and crystal orientation. In the case of (0 0 1) oriented crystals, the extent of material pile-up is low in Ag, compared to that in the Au and Ni crystals. The material pile-up profiles are conventional three-lobes shapes. However, for indents in (0 1 1) crystals, butterfly shaped pile-up profiles are observed in Ni, compared to conventional pile-up profiles in Au and Ag. In contrast, flower shaped pile-up profiles are observed in (1 1 1) Ni crystals, compared to conventional pile-up profiles in Au and Ag. Displacement bursts are also shown to occur in (0 1 1) and (1 1 1) oriented Ni at indentation load levels of ∼80–100 μN. These are attributed to the initial onset of dislocation slip activity, when the shear stress exceeds the estimated theoretical shear strengths of the materials.

Simulation of rolling textures of b.c.c. metals considering grain interactions and crystallographic slip on {110}, {112} and {123} planes

The rolling textures of b.c.c. transition metals are simulated using a Taylor-type model which takes into account grain interactions and allows for the activation of dislocation slip on {110}, {112} and {123} glide planes. Whereas in the so-called relaxed constraints Taylor models some strain constraints are dropped, in the grain interaction approach the degree of shear strain relaxation depends on the resulting gain in deformation energy. The simulations are carried out within the range ε = 0% to ε = 90%. The predicted textures are in good accord with experiment.